Note: Descriptions are shown in the official language in which they were submitted.
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ACTUATING MECHANISM FOR OPERATING A CIRCUIT BREAKER
DESCRIPTION
TECHNICAL FIELD
The invention relates to the field of high-voltage circuit breakers for
switchgears. More particularly, the invention relates to an actuating
mechanism for a
circuit breaker in a switchgear. The invention also relates to a method of
operating a
circuit breaker.
PRIOR ART
Actuating mechanisms for high-voltage (HV) circuit breakers are well-known.
These often take the form of (purely) mechanical devices having numerous
components,
such as gears, levers, springs, cam, freewheels etc., which carry high loads
and have
complex movement, making them prone to failure. Attempts to make these
components
stronger has been met with limited success, as the cost of new or lighter
materials is
generally prohibitive, and so they often end up heavier and in turn require
more energy
to operate the circuit breaker. There is also the matter of the actuating
mechanism being
susceptible to corrosion being made largely of metal. Maintenance of such
mechanical
actuating mechanisms is therefore expensive.
Hydraulic actuating mechanisms are also known. These typically possess a
piston for opening and closing the circuit breaker, the piston deriving its
energy through
hydraulic fluid passages from an accumulator. Hydraulic actuating mechanisms
not only
allow large loads to be developed and transmitted, they generally have fewer
components and less complex movement compared to their mechanical
counterparts.
Unfortunately however, a leak in the hydraulic fluid passage may cause a loss
of energy
being transferred from the accumulator, meaning that the actuating mechanism
is unable
to open the circuit breaker or may open it too slowly, which could be
dangerous.
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As such, there is a need for an actuating mechanism for a circuit breaker
which is reliable, has a lower part count and less complex movement, and is
cheaper.
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to an actuating mechanism for a circuit breaker
comprising an opening accumulator comprising a first piston, a first cylinder
and a first
compressible member, the first piston being movable in the first cylinder,
against the
force of the first compressible member, from a discharged position to a
charged position
by admitting hydraulic fluid, and movable to return, under the force of the
first
compressible member, to the discharged position by releasing the hydraulic
fluid,
wherein the first piston is directly mechanically connected to the first
compressible
member, and wherein the first cylinder is connected to an outlet fluid passage
which can
be opened and closed, the actuating mechanism further comprising a closing
accumulator
comprising a second piston, a second cylinder and a second compressible
member, the
second piston being movable in the second cylinder, against the force of the
second
compressible member, from a discharged position to a charged position by
admitting
hydraulic fluid, and to return, under the force of the second compressible
member, to the
discharged position by releasing the hydraulic fluid, wherein the first
cylinder and the
second cylinder are connected by an interconnecting fluid passage which can be
opened
and closed, arranged such that when the outlet fluid passage is closed and the
interconnecting fluid passage is opened, hydraulic fluid released from the
second cylinder
will be admitted into the first cylinder to move the first piston to the
charged position.
The present invention also relates to a method of operating the
abovementioned actuating mechanism.
Preferable features of the invention are defined in the appendant claims.
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BRIEF DESCRIPTION OF THE FIGURES
The invention will be better understood when reading the following detailed
description and non-limiting examples, as well as studying the figures,
wherein:
Figure 1 shows a cross-section view of an actuating mechanism for a circuit
breaker according to a preferred embodiment of the invention, with the first
piston and
the second piston in the discharged position,
Figure 2 shows a cross-section view of the same actuating mechanism, with
the first piston in the discharged position and the second piston in the
charged position,
Figure 3 shows a cross-section view of the same actuating mechanism, with
the first piston in the charged position and the second piston in discharged
position, and
Figure 4 shows a cross-section view of the same actuating mechanism, with
the first piston and the second piston in the charged position.
In all of these figures, identical references can designate identical or
similar
elements. In addition, the various portions shown in the figures are not
necessarily shown
according to a uniform scale, in order to make the figures more legible.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
Figures 1-4 show an actuating mechanism 30 for a high-voltage (HV) circuit
breaker 7 according to a preferred embodiment of the invention in various
states of
operation. It is connected, as shown in a rather simplified manner, to a
circuit breaker 7
of a switchgear 5. Referring initially to figure 1, the actuating mechanism 30
comprises an
opening accumulator 10 and a closing accumulator 20. The opening accumulator
10
comprises a first piston 11, a first cylinder 14 and a first spring 15, with
the first piston 11
slidably mounted in the first cylinder 14 and movable between a discharged
position
(shown in figure 1) and a charged position (shown in figure 3).
The first piston 11 further comprises a first piston rod 12. When the first
piston 11 is in the charged position, the first piston 11 and the first piston
rod 12 are
extended, and when the first piston 11 is in the discharged position, the
first piston 11
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and the first piston rod 12 are retracted. The first piston 11 also comprises
a first flange
13 for receiving a spring.
The first spring 15 exerts an axial force on the first piston 11, urging it
towards
the discharged position (shown in figure 1). It acts through the first flange
13 on which
the first spring 15 sits. The first piston 11 is directly mechanically
connected to the first
spring 15. Movement of the first piston 11 towards the charged position causes
the first
spring 15 to be compressed, and the resulting force acting on the first piston
11 to
increase.
The first cylinder 14 comprises an inlet 16 and an outlet 17 for admitting and
releasing hydraulic fluid respectively. When hydraulic fluid is admitted into
the first
cylinder 14, hydraulic pressure is applied to the first piston 11 and it moves
to the
charged position, against the force of the first spring 15. Equally, when the
hydraulic fluid
is released from the first cylinder 14, hydraulic pressure is removed from the
first piston
11 and it moves to return to the discharged position, under the force of the
first spring
15. The first piston 11 is arranged to be directly mechanically connected to
the circuit
breaker 7.
The actuating mechanism 30 also comprises a closing accumulator 20. In so
far as the features above are concerned, it is near identical to the opening
accumulator
10, the main difference in this particular embodiment being that it comprises
a stiffer
spring 25. For completeness, the closing accumulator 20 will also be described
here.
The closing accumulator 20 comprises a second piston 21, a second cylinder
24 and a second spring 25, with the second piston 21 slidably mounted in the
second
cylinder 24 and movable between a discharged position (shown in figure 1) and
a charged
position (shown in figure 2).
The second piston 21 further comprises a second piston rod 22. When the
second piston 21 is in the charged position, the second piston 21 and the
second piston
rod 22 are extended, and when the second piston 21 is in the discharged
position, the
second piston 21 and the piston rod 22 are retracted. The second piston 21
also
comprises a second flange 23 for receiving a spring.
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The second spring 25 exerts an axial force on the second piston 21, urging it
towards the discharged position (shown in figure 1). It acts through the
second flange 23
on which the second spring 25 sits. As much as possible, the second piston 21
is also
directly mechanically connected to the second spring 25 (which is shown in the
figures).
5 Movement of the second piston 21 towards the charged position causes the
second
spring 25 to be compressed, and the resulting force acting on the second
piston 21 to
increase.
The second cylinder 24 comprises an inlet 26 and an outlet 27 for admitting
and releasing hydraulic fluid respectively. When hydraulic fluid is admitted
into the
second cylinder 24, hydraulic pressure is applied to the second piston 21 and
it moves to
the charged position, against the force of the second spring 25. Equally, when
the
hydraulic fluid is released from the second cylinder 24, hydraulic pressure is
removed
from the second piston 21 and it moves to return to the discharged position,
under the
force of the second spring 25.
A pump 40 is provided on an inlet fluid passage 41 connected to the inlet 26
of the second cylinder 24. When the pump 40 is activated, hydraulic fluid is
pumped into
the second cylinder 24. When it is deactivated, hydraulic fluid is not pumped
into the
second cylinder 24.
A pump switch 45 is provided for operating the pump 40. It is arranged to
remain switched on unless acted on by a force. For example, the pump switch 45
may
comprise a spring urging it closed. This pump switch 45 is provided at a
location where
the second piston rod 22 does not act on the pump switch 45 unless it is in
the extended
position where it pushes the pump switch 45 open to switch it off. In other
words,
hydraulic fluid is pumped into the second cylinder 24 whenever the second
piston 21 is
not in the charged position. A reservoir 49 with hydraulic fluid is provided
from which the
pump 40 can draw hydraulic fluid and to which hydraulic fluid can be returned.
An interconnecting fluid passage 35 connects the outlet 27 of the second
cylinder 24 and the inlet 16 of the first cylinder 14. It allows the hydraulic
fluid released
from the second cylinder 24 to be admitted into the first cylinder 14. As
alluded to before,
the hydraulic pressure in the second cylinder 24 when the second piston 21 is
in the
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charged position is higher than that of the first cylinder 14 when the first
piston 11 is in
the discharged position. When the interconnecting fluid passage 35 is opened,
second
piston 21 will move to the discharged position, pumping the hydraulic fluid
into the first
cylinder 14 and moving the first piston 11 to the charged position. This
pressure
differential is realised by the second spring 25 being stiffer than the first
spring 15.
Although the first spring 15 and the second spring 25 are of the coil spring
type, it will be appreciated that other types of springs may be employed, such
as bellow
springs. It will equally be appreciated that while first compressible member
is ideally a
spring, this may not always be the case. The same applies to the second
compressible
member. It should also be noted that 'compressible members' are mechanical in
nature
and do not include 'compressible fluid' devices such as nitrogen accumulators.
A valve 38 is provided, located on the interconnecting fluid passage 35. It is
also located on an outlet fluid passage 37, which connects the outlet 17 of
the first
cylinder 14 to the hydraulic fluid reservoir 49. It is arranged to open and
close the
interconnecting fluid passage 35 and the outlet fluid passage 37 in opposite
fashion. This
valve 38 can be selectively operated to open and close the circuit breaker 7.
In figure 1,
the valve 38 is in the open position, i.e. corresponding to the circuit
breaker 7 being open,
while in figure 3, it is in the closed position, i.e. corresponding to the
circuit breaker 7
being closed. In the open position, hydraulic fluid can flow through the
outlet fluid
passage 37 but not through the interconnecting fluid passage 35, and in the
closed
position, hydraulic fluid can flow through the interconnecting fluid passage
35 but not the
outlet fluid passage 37. It will be understood that other valve arrangements
are possible,
for example, a separate valve on each of the interconnecting fluid passage 35
and the
outlet fluid passage 37.
The first piston 11 will now be discussed in further detail. As mentioned
above, first spring 15 exerts a force on the first piston 11 via the first
flange 13. There is
therefore a direct mechanical connection between the first spring 15, i.e. the
energy
storage device of the opening accumulator 10, and the first piston 11, and not
a fluidic
connection/hydraulic passage between the two. In use, the first piston 11 will
be directly
mechanically connected to the circuit breaker 7, typically through its piston
rod 12. This
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represents a direct mechanical connection between the first
spring/compressible
member 15 and the circuit breaker 7. It is further intended that the first
piston 11 in use
be connected to the circuit breaker 7 such that when the first piston 11 is in
the charged
position, the circuit breaker 7 is closed, and when it is in the discharged
position, the
circuit breaker 7 is open.
Therefore, when the first piston 11 is in the charged position, the compressed
first spring 15 stands ready to directly mechanically transfer its energy to
the first piston
11 to open the circuit breaker 7. Crucially, the energy for opening the
circuit breaker 7 is
not transferred through a fluidic connection/hydraulic passage as in the prior
art, which
as mentioned earlier may be prone to leak.
The actuating mechanism 30 has a housing 31 within which are located the
opening accumulator 10 and the closing accumulator 20, in parallel
orientation. The first
cylinder 14 and second cylinder 24 are provided near one axial end of the
housing 31. The
first piston 11 and second piston 21 are located in their respective
cylinders, although the
first piston rod 12 and second piston rod 22 protrude from the housing 31 at
an opposing
axial end, in particular from an end wall 32 of the housing 31. The
interconnecting fluid
passage 35 is also located in the housing 31. The first spring 15 and second
spring 25 are
respectively mounted around the first piston rod 12 and second piston rod 22,
between
the end wall 32 of the housing 31 and the respective first flange 13 and
second flange 23.
At least the first piston rod 12 is provided with a stop 18, located within
the housing 31,
for engaging the end wall 32 and preventing it moving beyond the charged
position. The
housing 31 may further house the pump 40 and the outlet fluid passage 37.
In this preferred embodiment, the pressure differential across the
interconnecting fluid passage 35 is realised by the second spring 25 being
stiffer than the
first spring 15. However, it will be appreciated that other arrangements may
allow the
same effect. For example, the first and second cylinders 14, 24 may be of
different sizes
or cross-sectional area, or the first and second compressible members 15, 25
may be
preloaded differently, etc. The important thing is that hydraulic fluid
released from the
second cylinder 24 is able to move the first piston 11 to the charged
position.
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The actuating mechanism 30 may of course comprise other features known in
the field. For example, 0-rings 39 are provided at the mouth of the cylinders
14, 24 so
that they seal against their pistons 11, 21 and prevent hydraulic fluid
leaking out.
Damping valves 33 may be provided to slow the pistons 11, 21 as they approach
the
discharged position. Flow adjustment valves 34 may be provided in the various
fluid
passages 35, 37 to adjust the opening and closing operation speed of the
circuit breaker.
The terms 'charged position' and 'discharged position' of the pistons used in
the foregoing correspond to whether energy has been respectively stored or
released
from their springs. Meanwhile, the terms 'opening accumulator' and 'closing
accumulator' correspond to the actuating operation they conduct on the circuit
breaker
when their stored energy is released.
To facilitate understanding of the invention, the operation of the actuating
mechanism in the context of a circuit breaker 7 in a switchgear 5 will be
briefly discussed,
with reference to figures 1-4. The first piston 11 is directly mechanically
connected to the
circuit breaker 7 and such that in the charged position the circuit breaker 7
is closed and
in the discharged position the circuit breaker 7 is open.
In figure 1, the actuating mechanism 30 is in the initial position. The first
piston 11 and the second piston 21 are in the discharged position, while the
circuit
breaker 7 is in the open position. We note that the pump switch 45 is in the
closed
position. The pump 40 is therefore activated and pumps hydraulic fluid through
inlet fluid
passage 41 from the reservoir 49 into the second cylinder 24. We note that the
valve 38 is
in the open position, and so the interconnecting fluid passage 35 is closed,
meaning that
hydraulic fluid being admitted into the second cylinder 24 is prevented from
being
released, and thus begins filling (or 'charging') the second cylinder 24. As a
result, the
second piston 21 moves from its discharged position towards the charged
position and
compresses the second spring 25. At the same time, the piston rod 22 of the
second
piston 21 extends towards the pump switch 45.
Figure 2 shows the state where the second piston 21 is in the charged
position. The second piston rod 22 has pushed the pump switch 45 to switch it
off,
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thereby deactivating the pump 40. The second spring 25 maintains the hydraulic
pressure
in the second cylinder 24. The circuit breaker 7 is presently still in the
open position.
When the circuit breaker 7 is to be closed, the valve 38 is moved to the
closed
position. This opens the interconnecting fluid passage 35, allowing hydraulic
fluid to be
released from the second cylinder 24 under the force of the second spring 25.
The
hydraulic fluid flows through the interconnecting fluid passage 35, and is
admitted into
the first cylinder 14. Concurrently, the valve 38 has closed the outlet fluid
passage 37,
meaning that the hydraulic fluid admitted into the first cylinder 14 is
prevented from
being released, and thus begins filling the first cylinder 14.
As the second spring 25 is stiffer than the first spring 15 and is compressed,
the hydraulic pressure in the second cylinder 24 is higher than that of the
first cylinder 14.
The second piston 21 thus moves rapidly to the discharged position, causing in
turn the
first piston 11 to move rapidly to the charged position and the first piston
rod 12 to
extend to move the circuit breaker 7 from the open position to the closed
position,
thereby allowing current to flow from the switchgear 5 to the grid.
Figure 3 shows the actuating mechanism 30 (just) after the circuit breaker 7
has been closed. With the second piston 21 now in the discharged position, the
pump
switch 45 is switched on, meaning the pump 40 is activated and begins pumping
hydraulic
fluid into the second cylinder 24 again until the second piston 21 reaches the
charged
position. We note that the stop 18 on the first piston 11 is engaged with the
end wall 32
of the housing, which prevents the first piston 11 moving beyond its charged
position.
Limiting the stroke of the first piston 11 in this way not only allows the
second cylinder 24
to be filled without moving the first piston 11, it also defines the stroke of
the first piston
11 allowing precise control of the of the circuit breaker 7. A stop may
optionally be
provided on the second piston rod 22 too.
Finally, figure 4 shows the main operational state of the actuating mechanism,
wherein the first piston 11 and the second piston 21 are both in the charged
position. As
can be seen, the circuit breaker 7 is closed, although the first piston 11 is
ready to open
the circuit breaker 7 if necessary. Meanwhile, the second piston 21 is ready
to close the
circuit breaker 7 again (should it be opened).
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When a fault is detected and the circuit breaker 7 needs to be opened, the
valve 38 is moved to the open position. This opens the outlet fluid passage 37
while
concurrently closing the interconnecting fluid passage 35, allowing hydraulic
fluid to be
released from the first cylinder 14 to the reservoir 49. The first piston 11
will rapidly
5 return from the charged position to the discharged position, the energy
released from the
first spring 15 being directly mechanically transferred to the circuit breaker
7 to open it,
with the first piston rod 12 retracting in the process to move the circuit
breaker 7 from
the closed position to the open position, thereby preventing current from
flowing from
the switchgear 5 to the grid.
10 At this point, the actuating mechanism 30 is effectively in the
state as shown
in figure 2, and will typically need to cycle through the states shown in
figure 3 and figure
4 to revert to the main operational state (with the circuit breaker 7 closed).
The present invention provides a unique actuating mechanism which cleverly
combines aspects of mechanical actuating mechanisms and hydraulic actuating
mechanisms, retaining their advantages while doing away with their
disadvantageous.
Like known mechanical actuating mechanisms, the actuation mechanism of
the present invention comprises a direct mechanical connection from the
compressible
member for opening the circuit breaker to the component for operating the
circuit
breaker. It is however of simpler construction, having far fewer components
and less
complex movement when compared to known mechanical actuating mechanisms, and
as
such is less likely to fail and has reduced maintenance cost. By employing
hydraulics, large
forces can be developed easily, and thus the energy for operating the circuit
breaker can
readily be provided. Furthermore, it will be appreciated that many of its
moving
component, in use, are in contact with hydraulic fluid, maintaining them
lubricated and
mitigating corrosion.
At the same time, the actuating mechanism of the present invention has
increased reliability when compared to known hydraulic actuating mechanisms,
as there
is a greatly reduced risk of the circuit breaker not opening or opening too
slowly.
Importantly, this actuating mechanism provides a direct mechanical connection
from the
compressible member to the piston for opening the circuit breaker. All the
energy stored
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in the compressible member can therefore be utilised to open the circuit
breaker,
ensuring that the circuit breaker can always be opened. This is unlike known
hydraulic
actuating mechanisms where a leak in the hydraulic passage may cause a loss of
energy
being transferred to the piston for opening the circuit breaker. This
actuating mechanism
of the present invention thus has improved reliability and safety.
In one variant of the present embodiment, instead of being compressed when
the pistons are in the charged position, the compressible members are provided
such that
they are stretched when hydraulic fluid is admitted into the cylinders and the
pistons are
in the charged position. Such a variant can be visualised with the springs of
the preferred
embodiment being provided within the cylinders and connecting the pistons to
the
cylinders such that they resist the extension of the pistons. Other
modifications will be
apparent to the skilled person in light of the disclosure above.
